Increasingly, customers are interested in using their mobile phone as the key to the vehicle. In the near term, Phone-as-a-Key (PaaK) systems will likely employ BLE technology exclusively to detect and localize portable devices since BLE is widely available on portable devices and is ultra-low power.
A modern practical device localization method involves determining distance by measuring RSSI. However, determining distance via RSSI at the frequency of BLE (i.e. 2.4 GHz) presents several challenges, the most significant of which is multipath fading. A relative immunity to multipath fading can be achieved by using other measurements.